This invention relates to the continuous casting of aluminum deoxidized steels and more particularly to the feeding of the aluminum wire to a continuous casting mold without the formation of oxide inclusions.
It has long been known that the addition of aluminum to iron or steel will deoxidize the molten metal as was taught by U.S. Pat. No. 1,035,947, at least as early as 1912. Conventionally, aluminum can be added in the form of shot or granules and can be fed continuously by a screw feeder. An alternative feeding method is shown by Leupold in U.S. Pat. No. 3,331,680 in which aluminum wire is fed through a guide tube into a molten metal pouring stream. Injection of aluminum wire into steel during the casting procedure results in a deoxidized or aluminum killed steel. If aluminum is added to the molten metal in the ladle or the tundish, fine aluminate deposits form on the metering nozzles, eventually plugging the nozzles and shutting off flow of steel to the mold. Hence the need developed to add aluminum beneath the tundish. Leupold feeds his aluminum wire directly into the tundish stream which causes some turbulence and additional oxide entrainment. The prevention or reoxidation at the region of contact of the steel by the aluminum wire is of primary importance. If reoxidation at this location occurs there is a high probability that viscous manganesealumino-silicate inclusions will be formed, and entrapped on or immediately below the surface of the casting. Such inclusions can be major problems in subsequent processing of the steel casting. When aluminum wire is fed into the molten steel pouring stream in the invented system, the formation of harmful inclusions due to reoxidation is severely limited.
Aluminum has an extremely high affinity of oxygen. It will react with oxygen from air first, then with oxygen in steel. Thus it is important to exclude atmospheric oxygen from the environment adjacent to the steel stream. Experimentation has resulted in the development of an aluminum wire feeding system in conjunction with a continuous casting shroud which shrouds the molten metal during the pouring from the tundish into the mold.
A suitable feeder is available from Linde Division of Union Carbide.